U.S. patent number 5,999,352 [Application Number 08/857,519] was granted by the patent office on 1999-12-07 for variable bits per inch recording.
This patent grant is currently assigned to Seagate Technology, Inc.. Invention is credited to Myint Ngwe, Say Kwee Teck, Quak Beng Wee.
United States Patent |
5,999,352 |
Teck , et al. |
December 7, 1999 |
Variable bits per inch recording
Abstract
A disc drive and a method of storing data using the disc drive
are disclosed. Multiple data heads are each supported adjacent a
corresponding one of multiple disc surfaces of a disc stack to form
multiple head/media combinations. A separate guardband or recording
density capability for each of the multiple head/media combinations
is determined. An actual recording density is assigned to each of
the multiple head/media combinations based upon the recording
density capability for the particular head/media combination. The
actual recording density assigned to each of the multiple
head/media combinations can be different from the actual recording
densities assigned to other head/media combinations. The disc drive
is controlled such that data is recorded on each of the surfaces at
the actual recording density assigned thereto.
Inventors: |
Teck; Say Kwee (Singapore,
SG), Wee; Quak Beng (Singapore, SG), Ngwe;
Myint (Singapore, SG) |
Assignee: |
Seagate Technology, Inc.
(Scotts Valley, CA)
|
Family
ID: |
26713404 |
Appl.
No.: |
08/857,519 |
Filed: |
May 16, 1997 |
Current U.S.
Class: |
360/48; 360/51;
G9B/5.024; G9B/5.157 |
Current CPC
Class: |
G11B
5/012 (20130101); G11B 5/4886 (20130101); G11B
5/09 (20130101) |
Current International
Class: |
G11B
5/012 (20060101); G11B 5/48 (20060101); G11B
5/09 (20060101); G11B 005/09 () |
Field of
Search: |
;360/75-76,51,48,104,106-107,119-121 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sniezek; Andrew L.
Assistant Examiner: Davidson; Dan I.
Attorney, Agent or Firm: Westman, Champlin & Kelly,
P.A.
Parent Case Text
The present application claims the benefit of earlier filed U.S.
Provisional Application No. 60/036,701, entitled "VARIABLE BPI
(BITS PER INCH) RECORDING", filed on Jan. 31, 1997.
Claims
What is claimed is:
1. A method of storing data in a disc drive having a plurality of
magnetic data heads each supported adjacent a corresponding one of
a plurality of disc surfaces of a disc stack to form a plurality of
head/surface combinations, the method comprising:
determining a separate guardband recording density for each of the
plurality of head/surface combinations, wherein determining the
separate guardband recording density for each of the plurality of
head/surface combinations comprises:
determining a separate avalanche recording density for each of the
plurality of head/surface combinations, wherein the avalanche
recording density for each of the plurality of head/surface
combinations is the recording density above which a predetermined
maximum error threshold for the disc drive will be exceeded;
and
subtracting a design margin recording density for the disc drive
from each of the separate avalanche recording densities to
determine the guardband recording density for each of the plurality
of head/surface combinations;
assigning an actual recording density to each of the plurality of
head/surface combinations based upon the guardband recording
density for the particular head/surface combination such that the
actual recording density assigned to each head/surface combination
does not exceed the guardband recording density for the particular
head/surface combination, and such that a total effective net
capacity change of the disc drive is equal to zero, wherein the
total effective net capacity change of the disc drive is equal to a
summation of the difference, for each head/surface combination,
between the actual recording density for each head/surface
combination and an effective recording density selected for the
disc drive, wherein assigning the actual recording density for each
of the plurality of head/surface combinations results in different
ones of the plurality of head/surface combinations having different
recording densities assigned thereto; and
controlling the disc drive such that data is recorded on each of
the surfaces at the actual recording density assigned thereto.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to disc drive data storage
systems having multiple discs mounted on a spindle to form a disc
stack. More particularly, the present invention relates to a disc
drive data storage system in which data is recorded on different
surfaces of the disc stack at different recording densities in
order to optimize the performance of the disc drive.
A typical disc drive data storage system can include multiple
magnetic discs mounted for rotation on a hub or spindle. A spindle
motor causes the discs to spin and the surface of the discs to pass
under respective head gimbal assemblies (HGAs). The HGAs carry
transducers which write information to, and read information from
the disc surfaces. An actuator mechanism moves the HGAs from track
to track across surfaces of the discs under control of electronic
circuitry. Read and write operations are performed through a
transducer which is carried in a slider body. The slider and
transducer are sometimes collectively referred to as a head, and
typically a single head is associated with each disc surface. The
heads are selectively moved under the control of electronic
circuitry to any one of multiple circular, concentric data tracks
on the corresponding disc surface by an actuator device. Each
slider body includes an air bearing surface (ABS). As the disc
rotates the disc drags air beneath the ABS, which develops a
lifting force which causes the head to lift and fly several
microinches above the disc surface.
In existing disc drive systems, one of the parameters which
dictates the AREAL density is the recording density, typically
designated in bits per inch (BPI). Recording density is a
predetermined parameter at the disc drive design stage. All disc
surfaces in the disc stack are set to one standard recording
density or BPI value. The maximum recording density is usually
determined by the available head, disc surface and read channel
capabilities. To ensure the maximum production yield and read
channel margin, this recording density is usually set at a point
where the drive still has sufficient read channel margin under the
worst case combination of head, media (i.e., disc surface) and read
channel distribution.
This current recording density scheme results in the margin
available not being maximized for good head/media surface
combinations, while stressing the available channel margin for the
worst head/media combinations. In a multiple disc pack drive, by
probability, there will virtually always be the situation where the
various head/media combinations have different margins available. A
single low margin head/media combination will usually result in the
disc drive not meeting the desired drive error rate, even though
all other head/media combinations in the disc drive may exceed the
required channel margin.
SUMMARY OF THE INVENTION
A disc drive and a method of storing data using the disc drive are
disclosed. Multiple data heads are each supported adjacent a
corresponding one of multiple disc surfaces of a disc stack to form
multiple head/media combinations. A separate guardband or recording
density capability for each of the multiple head/media combinations
is determined. An actual recording density is assigned to each of
the multiple head/media combinations based upon the recording
density capability for the particular head/media combination. The
actual recording density assigned to each of the multiple
head/media-combinations can be different from the actual recording
densities assigned to other head/media combinations. The disc drive
is controlled such that data is recorded on each of the surfaces at
the actual recording density assigned thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a portion of a disc drive according to
the present invention.
FIG. 2 is a plot illustrating typical variations of head/media
surface combination recording density margin capabilities for six
head/media surface combinations within a disc pack.
FIG. 3 is a flow diagram illustrating a preferred method of
controlling the disc drive of the present invention such that the
actual recording density for each of the plurality of head/media
combinations can be different from the recording densities of other
head/media surface combinations.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a block diagram of disc drive according to the present
invention. Disc drive 10 includes drive controller 12, memory 14,
disc stack assembly 16, actuator assembly 18 and read channel 20.
Drive controller 12 is typically a microprocessor or digital
computer, and is coupled to a host system which instructs
controller 12 to store data on, and retrieve data from, disc stack
16.
Memory 14 can be any of a variety of well known data storage
devices capable of storing data for use by controller 12. Also,
memory 14 can include a combination of different types of memory
devices such as read only memory (ROM) and volatile or non-volatile
random access memory (RAM). In preferred embodiments, memory 14
stores the firmware programming used by drive controller 12 in
order to implement the variable recording density aspects of the
present invention.
Disc stack assembly 16 includes spindle 26 which supports multiple
coaxially arranged discs 30, 32 and 34. The discs are mounted for
rotation with spindle 26 about axis of rotation 28. Each of the
discs has a first surface and a second surface. First disc 30 has
first surface 36 and second surface 38. Second disc 32 has first
surface 40 and second surface 42. Third disc 34 has first surface
44 and second surface 46. All of surfaces 36, 38, 40, 42, 44 and 46
include concentric tracks for receiving and storing data in the
form of flux reversals encoded on the tracks.
A group of tracks which include one track on each of surfaces 36,
38, 40, 42, 44 and 46, wherein each track in the group is located a
common radial distance from the inner diameter of the corresponding
disc upon which is resides, is referred to as a cylinder. In the
prior art, the recording density at which data was stored in a
particular cylinder was a predetermined fixed value, regardless of
disc surface or media on which the various data tracks resided. As
is discussed below in greater detail, the present invention
optimizes the performance of drive 10 by recording data on various
disc surfaces of a particular cylinder at differing recording
densities, determined by the recording density capability for the
particular surface and its corresponding data read. In general,
with the present invention, a recording density is determined
separately for each disc surface and used throughout the disc
surface.
Actuator assembly 18 includes actuator 48 supporting multiple
actuator arms 50. Each of actuator arms 50 is rigidly coupled to at
least one head assembly 52. Each head assembly 52 includes a load
beam, or a flexure arm, rigidly coupled to actuator arm 50 at a
first end, and to a suspension or gimbal at a second end. The
suspension is, in turn, coupled to a hydrodynamic air bearing which
supports a data head (i.e., data heads H0, H1, H2, H3, H4 and H5)
above the corresponding disc surface. Each data head typically
includes a read transducer and a write transducer carried by a
slider. As shown, data heads H0, H1, H2, H3, H14 and H5 are
supported adjacent respective medias or surfaces 36, 38, 40, 42, 44
and 46.
Actuator 48 is rotatably mounted with respect to discs 30, 32 and
34. Actuator 48 typically includes a voice coil which interacts
with a magnet to produce the selective rotation of actuator 48. As
actuator 48 rotates, it moves the transducers coupled to the head
assemblies either radially inward or radially outward on the discs.
In this way, actuator 48 positions the transducers on the various
heads over a desired track (and cylinder) on the corresponding
discs.
Read channel 20 is electrically coupled to each of heads H0, H1,
H2, H3, H4 and H5 and carries signals read by various heads from
their corresponding disc surfaces to a host system which has
instructed disc drive 10 to retrieve the data. Also, read channel
20 can carry servo signals read by one or more of the heads from a
servo data track. As is known in the art, the servo position
information can be provided to drive controller 12 and used to
control actuator assembly 18 to achieve head positioning over a
desired cylinder. Read channel 20 can also include other
components, for example amplifiers and filters, for conditioning
the read back signal. In the prior art, the recording density
(sometimes referred to as maximum BPI or bits per inch) for all
medias or disc surfaces is usually determined by the available
head, media and read channel capabilities. To ensure maximum
production yield and read channel margin, this recording density
for the disc drive is usually set at a point where the drive still
has sufficient read channel margin under the worst combination of
head, media and read channel distribution. This conventional scheme
results in not maximizing the margin available with good head/media
combinations, while stretching the available channel margin for the
worst head/media combinations. In a disc drive having multiple
discs, and therefore having multiple head/media-combinations, the
situation usually exists where the various head/media combinations
have different recording density capabilities, and thus different
margins. A single head/media combination having a low margin
frequently results in the disc drive not meeting the desired drive
error rate, even though all other head/media combinations in the
drive may exceed the channel margin.
FIG. 2 is a plot which illustrates the typical variation of
head/media margin capability within a disc pack. The plot of FIG. 2
shows the capability (measured by the total number of errors
detected) as the recording density (in KBPI) increases, for six
head/media combinations. The curve designated as "H0 Total"
represents the total number of errors, as a function of recording
density, for the combination of the Head H0 and disc surface 36.
The curve designated as "H1 Total" represents the total number of
errors for the head/media combination of head H1 and disc surface
38. The curve designated as "H2 Total" represents the total number
of errors for the head/media combination of head H2 and disc
surface 40. The curve designated as "H3 Total" represents the total
number of errors for the head/media combination of head H3 and disc
surface 42. The curve designated as "H4 Total " represents the
total number of errors for the head/media combination of head H4
and disc surface 44. The curve designated as "H5 Total" represents
the total number of errors for the head/media combination of head
H5 and disc surface 46.
At the disc drive design stage, a bit error rate that the designers
deem acceptable is set. This maximum bit error rate is typically
referred to as an avalanche errors threshold. The avalanche KBPI or
avalanche recording density is the recording density for a
particular head/media combination when the avalanche errors
threshold is reached. The guardband KBPI or guardband recording
density is the maximum recording density a designer can use, taking
into account a predetermined design margin. In general, the
guardband recording density can be defined as the avalanche
recording density minus the desired design margin. The guardband
recording density can also be referred to as a design recording
density or a recording density capability.
Table 1 illustrates the avalanche recording density (in KBPI) and
the guardband recording density (in KBPI) for each head/media
combination illustrated in FIG. 1 for one typical disc drive
10.
TABLE 1 ______________________________________ Avalanche Guardband
Recording Recording Head #/ Density Density Disc Surface (KBPI)
(KBPI) ______________________________________ H2/40 107 97 H3/42
108 98 H5/46 110 100 H4/44 113 103 H1/38 115 105 H0/36 120 110
______________________________________
As can be seen from the differences between the avalanche recording
density and the guardband recording density for each head/media
combination illustrated in Table 1, a design margin of 10 KBPI is
assumed. As can further be seen in Table 1, the guardband recording
densities for the various head/media combinations range from 97
KBPI to 110 KBPI. If the recording density for a disc drive having
the distribution illustrated in Table 1 were set at 102 KBPI for
all disc surfaces, the head/media combinations corresponding to
heads H2, H3 and H5 will not have sufficient margin (i.e., the
recording density would surpass the guardband), while the
head/media combinations corresponding to heads H0, H1 and H4 will
have more than sufficient margin. In this case, the drive would
fail the required minimum margin requirement which is established
for the entire drive. Therefore, in the prior art, to ensure that
the drive would pass with the required guardband, the recording
density for all disc surfaces would be set at 97 KBPI. This scheme
is not efficient since it results in the drive performance being
determined by the worst case head/media combination in a disc
stack.
Disc drive 10 of the present invention overcomes this inefficiency
by setting the actual recording density for each individual
head/media combination based upon the head/media combination
recording density capability (i.e. according to the guardband
recording density for the head/media combination). This is
illustrated in Table 2.
TABLE 2 ______________________________________ Actual Delta to
Avalanche Guardband Record- Effective Hd Recording Recording ing
Recording #/Disc Density Density Density Density Surface (KBPI)
(KBPI) (KBPI) (102 KBPI) ______________________________________
H2/40 107 97 97 97 - 102 = -5 H3/42 108 98 98 98 - 102 = -4 H5/46
110 100 100 100 - 102 = -2 H4/44 113 103 102 102 - 102 = 0 H1/38
115 105 105 105 - 102 = +3 H0/36 120 110 110 110 - 102 = +8 0 net
capacity change ______________________________________
For the head/media combination of head H2 and disc surface 40, the
actual recording density is still set at 97 KBPI in order not to
violate the guardband recording density. However, for each of the
remaining five head/media combinations, the actual recording
density is increased from the 97 KBPI recording density which would
be used for all disc surfaces in the prior art. The recording
density for each head/media combination is set at a level which
does not violate the guardband for the particular head/media
combination.
The actual recording density for the head/media combination of head
H3 and disc surface 42 is set at 98 KBPI. The actual recording
density for the head/media combination of head H5 and disc surface
46 is set to the corresponding guardband of 100 KBPI. The actual
recording density for the head/media combination of head H1 and
disc surface 38 is set to the corresponding guardband of 105 KBPI.
The actual is recording density corresponding to the head/media
combination of head H0 and disc surface 36 is set to the
corresponding guardband recording density of 110 KBPI. The
head/media combination of head H4 and disc surface 44 is set 1 KBPI
below the guardband recording density of 103 KBPI, to 102 KBPI.
It is noted that, unlike the other head/media combinations, the
actual recording density for head H4 and disc surface 44 is not set
exactly to the corresponding guardband recording density.
Optimally, the actual recording density for each head/media
combination can be set to the corresponding guardband recording
density. However, the total drive capacity for the disc drive is
typically established by setting an effective recording density or
average recording density for the drive such that the net capacity
change is equal to zero. In other words, if an effective recording
density of 102 KBPI is set for disc drive 10, the summation of the
differences between the actual recording density of each head/media
combination and the effective recording density equals zero. For an
effective recording density of 102 KBPI for the disc drive, this is
shown in the last column of Table 2. For this reason, the actual
recording density for head H 4 and disc surface 44 was set in this
example to 102 KBPI instead of 103 KBPI. However, although the net
capacity change should always be zero, it is not necessary for the
effective recording density for the drive to be set to an integer
value. For example, if the effective recording density for the disc
drive were set to 102.167 KBPI, the actual recording density for
head H4 and disc surface 44 could also be set to the guardband
recording density of 103 KBPI. In this instance the net capacity
change from this new effective recording density would still be
zero for the disc drive. With an effective recording density for
the disc drive set to 102.167 KBPI, the delta to the effective
recording density for the head/media combination corresponding to
heads H2, H3, H5, H4, H1 and H0 would then be -5.167, -4.167,
-2.167, +0.833 (assuming Head H4 has an actual recordang density at
103 KBPI), +2.833, and +7.833, respectively.
The present invention ensures that the available margin for each
head/media combination of disc drive 10 is optimized. Head/media
combinations with more than adequate margin as indicated in the
plot of FIG.2 (i.e., heads H0, H1 and H4) can use a higher KBPI
setting. Heads/media combination (i.e., heads H2, H3, and H5) with
poor margin can use a lower KBPI setting. The overall capacity is
still maintained. This essentially results in shifting "extra"
margin available from heads H0, H1 and H4 to heads H2, H3 and H5.
The effect of the shift of margin from a good head/media
combination to a lower margin head/media combination results in the
design of disc drive 10 with a higher capacity than possible
without the present invention. In this case, the effective
recording density using the present invention can be 102 KBPI
instead of 97 KBPI as was the case in the prior art. This
represents an increase of 5 percent more capacity than otherwise
possible. Viewed another way, the present invention allows poorer
margin head/media combinations to be used on a drive which would
otherwise have failed because of only one head/media combination
having a poor margin.
The present invention is implemented in the software or firmware
programming of drive controller 12. This firmware can be stored in
associated memory 14. During the disc drive fabrication process,
the actual recording densities for each head/media combination are
determined and programmed into drive controller 12 and/or memory 14
in any of a variety of conventional manners. For example, this
information can be sent to controller 12 from a host system. In the
alternative, memory 14 can be a replaceable module which is
preprogrammed with the variable actual recording density
information prior to insertion into disc drive 10. Then, during
operation, drive controller 12 controls the recording density on
each disc surface in the manner described above. Typically, this
will mean that controller 12 controls actuator assembly 18 and the
corresponding heads to record data on each disc surface at a single
actual recording density established for that disc surface.
However, this can also mean that, for a given cylinder (i.e. set of
data tracks on each of the disc surfaces), the recording density of
the corresponding data tracks of the cylinder are set to differing
and unique values established for the particular head/media
combinations.
FIG.3 is a flow diagram which illustrates one preferred method in
which drive 10 of the present invention is controlled such that the
actual recording density for each of the head/media combination is
uniquely selected, often differing from the recording densities of
other head/media combinations. First, as represented at step 110, a
separate guardband recording density or recording density
capability for each of the head/media combinations is determined.
As discussed above, the guardband recording density can be defined
as the avalanche recording density minus a desired design
margin.
Next, as illustrated in step 120, an actual recording density is
assigned to each of the head/media combinations based upon the
recording density capability (i.e., guardband recording density)
for the particular head/media combination. The actual recording
density for each of the bead/media combinations can be different
from the recording densities of other head/media combinations if
the guardband recording densities are different. Finally, as
illustrated in step 130, controller 12 controls disc drive 10 such
that data is recorded on each of the disc surfaces at the actual
recording density assigned to the particular head/media
combination.
Although the present invention has been described with reference to
preferred embodiments, workers skilled in the art will recognize
that changes may be made in form and detail without departing from
the spirit and scope of the invention.
* * * * *